Can't zoom after pressing Numpad (.) on object - Blender 2.8
In 2.8+ the simplest fix is to go into Edit -> Preferences -> Navigation and enable "Auto Depth"

This will fix the zoom slow down issue, but does change it so your cursor placement affects the navigation. 

Since 2.8, some of the better responses have changed to this previously asked question and no longer work, or work differently.